为什么查询不直接使用key？

Question

我有一个复杂的查询：

SELECT * FROM `s` 
LEFT JOIN `users` AS `iu` ON iu.user_id = s.s_iu_id 
LEFT JOIN `users` AS `uu` ON uu.user_id = s.uu_id 
LEFT JOIN `sic` ON sic.s_id = s.s_id 
LEFT JOIN `users` AS `ppu` ON ppu.user_id = sic.pure_price_user_id 
LEFT JOIN `users` AS `spu` ON spu.user_id = sic.spu_id 
LEFT JOIN `us` ON f_user_id = 8714 AND users.f_s_id = s.s_id 
LEFT JOIN `c` ON c.c_id = sic.c_id 
LEFT JOIN `countries` ON countries.country_id = s.country_id 
LEFT JOIN `countries` AS `countries2` ON countries2.country_id = countries.parent_id 
LEFT JOIN `continents` ON continents.continent_id = countries.continent_id 
LEFT JOIN `countryperiods` ON countryperiods.countryPeriod_id = s.countryPeriod_id 
LEFT JOIN `currencies` ON currencies.currency_id = countryperiods.currency_id 
LEFT JOIN `serrations` AS `s1` ON s.serration_width_id = s1.id 
LEFT JOIN `serrations` AS `s2` ON s.serration_height_id = s2.id 
LEFT JOIN `colors` ON colors.color_id = s.color_id 
LEFT JOIN `colors` AS `c2` ON c2.color_id = s.background_id 
LEFT JOIN `colors` AS `c3` ON c3.color_id = s.color2_id 
WHERE (s.fsis_id = '141518') AND (sic.c_id = '1') AND 
((s.s_enabled = 1) OR (s.s_iu_id = '8714')) AND 
(s.s_exists = 1) 
ORDER BY `c_number` ASC, `cn_prepend` ASC, `cn_append` ASC 
LIMIT 10000

解释一下：

id  s_type  table          type       possible_keys            key            key_len   ref                            rows    Extra 
1   SIMPLE  sic            range      catNum,catalog_s_id      catalog_s_id   10        NULL                           132480  Using index condition; Using temporary; Using filesort
1   SIMPLE  ppu            eq_ref     PRIMARY                  PRIMARY        4         data.sic.pure_price_user_id    1       Using where
1   SIMPLE  spu            eq_ref     PRIMARY                  PRIMARY        4         data.sic.stamped_price_user_id 1       Using where
1   SIMPLE  s              eq_ref     PRIMARY,s_insertUser_id  PRIMARY        4         data.sic.s_id                  1       Using where
1   SIMPLE  us             ref|filter us,f_s_id,f_user_id      f_s_id|f_user_id  5|5    data.sic.s_id                  1 (0%)  Using where; Using rowid filter
1   SIMPLE  c              ALL        PRIMARY                  NULL           NULL  NULL                               2       Using where; Using join buffer (flat, BNL join)
1   SIMPLE  countries      ALL        PRIMARY                  NULL           NULL     NULL                            494     Using where; Using join buffer (incremental, BNL join)
1   SIMPLE  countries2     eq_ref     PRIMARY                  PRIMARY        4        data.countries.parent_id        1       Using where
1   SIMPLE  continents     eq_ref     PRIMARY                  PRIMARY        4        data.countries.continent_id     1       Using where
1   SIMPLE  countryperiods eq_ref     PRIMARY                  PRIMARY        4        data.s.countryPeriod_id         1       Using where
1   SIMPLE  iu             eq_ref     PRIMARY                  PRIMARY        4        data.s.s_insertUser_id          1       Using where
1   SIMPLE  uu             eq_ref     PRIMARY                  PRIMARY        4        data.s.uploadUser_id            1       Using where
1   SIMPLE  currencies     ALL        PRIMARY                  NULL           NULL     NULL                            281     Using where; Using join buffer (flat, BNL join)
1   SIMPLE  s1             eq_ref     PRIMARY                  PRIMARY        4        data.s.serration_width_id       1       Using where
1   SIMPLE  s2             eq_ref     PRIMARY                  PRIMARY        4        data.s.serration_height_id      1       Using where
1   SIMPLE  colors         eq_ref     PRIMARY                  PRIMARY        4        data.s.color_id                 1       Using where
1   SIMPLE  c2             eq_ref     PRIMARY                  PRIMARY        4        data.s.background_id            1       Using where
1   SIMPLE  c3             eq_ref     PRIMARY                  PRIMARY        4        data.s.color2_id                1       Using where

为什么表c、国家和货币在与其他表相同的连接时不使用主索引？我可以优化它吗？查询持续时间1.3883s。

Answer 1

将

sic.c_id = 1

从

where

子句移至

join

条件；将其放入

where

子句中会强制与

sic

的连接成为

INNER

连接。

还更改 ids 上的所有条件以与整数而不是字符串进行比较，例如

s.fsis_id = 141518

不是

s.fsis_id = '141518'

SELECT *
FROM `s` 
LEFT JOIN `users` AS `iu` ON iu.user_id = s.s_iu_id 
LEFT JOIN `users` AS `uu` ON uu.user_id = s.uu_id 
LEFT JOIN `sic` ON sic.s_id = s.s_id AND sic.c_id = 1
LEFT JOIN `users` AS `ppu` ON ppu.user_id = sic.pure_price_user_id 
LEFT JOIN `users` AS `spu` ON spu.user_id = sic.spu_id 
LEFT JOIN `us` ON f_user_id = 8714 AND users.f_s_id = s.s_id 
LEFT JOIN `c` ON c.c_id = sic.c_id 
LEFT JOIN `countries` ON countries.country_id = s.country_id 
LEFT JOIN `countries` AS `countries2` ON countries2.country_id = countries.parent_id 
LEFT JOIN `continents` ON continents.continent_id = countries.continent_id 
LEFT JOIN `countryperiods` ON countryperiods.countryPeriod_id = s.countryPeriod_id 
LEFT JOIN `currencies` ON currencies.currency_id = countryperiods.currency_id 
LEFT JOIN `serrations` AS `s1` ON s.serration_width_id = s1.id 
LEFT JOIN `serrations` AS `s2` ON s.serration_height_id = s2.id 
LEFT JOIN `colors` ON colors.color_id = s.color_id 
LEFT JOIN `colors` AS `c2` ON c2.color_id = s.background_id 
LEFT JOIN `colors` AS `c3` ON c3.color_id = s.color2_id 
WHERE s.fsis_id = 141518
AND (s.s_enabled = 1 OR s.s_iu_id = 8714)
AND s.s_exists = 1
ORDER BY `c_number`, `cn_prepend`, `cn_append` 
LIMIT 10000

（为了清楚起见，删除了不必要的括号）